barza21
15+ Year Contributor
- 147
- 46
- Oct 11, 2006
-
Fairbanks,
Alaska
Gentlemen,
I have a 91 TSI AWD 6 bolt with a manual trans, stock turbo, stock injectors, stock fuel system, stock boost levels. I rebuilt it about 1500 miles ago. It had a very bad idle surge problem that turned out to be the FIAV (I blocked it). I fixed that and then the car idled very good for about 500 miles. A different problem has risen.
At start up the car idles at 1500 rpm and slowly comes down to 1100 rpm when fully warm. At random times it dips down and idles at 750-800rpm how I had it set to previously, but after moving and coming back to a stop the idle goes back up to 1100. The timing is set correctly to what the manual calls out for (5* btdc, I think). Here is the interesting part, if I ground the pin in the cabin and in the engine bay for idle adjustment, the car idles perfect at 750-800 rpm. As soon as I disconnect one of the grounding wires, it jumps back up to 1100 rpm. This led me to believe that maybe the idle position switch could be bad, so I checked voltage and ohms. Botch checked ok. With tb closed I'm getting about 1.5-3.0 ohms. WIth the throttle cracked open it goes to infinity (the DMM). The voltage is at about 0.0 vdc when closed and 12.xx vdc when open. I did a boost leak and it checked out good. I also tried grounding the idle position switch wire directly, but that didn't change the idle condition. It remained at 1100 rpm.
My question is: what could be causing the ECU to not go into idle mode? What components do the ECU listen to to determine it's at idle? The IPS checks ok, the TPS is set correctly.
One interesting fact: When the ignition key is to on (the engine not running) , I can hear the ISC motor chattering away. The only way that I have gotten it to stop was to disconnect it. It does this at random before I start it a lot of times.
Thank you for all your help!
I have a 91 TSI AWD 6 bolt with a manual trans, stock turbo, stock injectors, stock fuel system, stock boost levels. I rebuilt it about 1500 miles ago. It had a very bad idle surge problem that turned out to be the FIAV (I blocked it). I fixed that and then the car idled very good for about 500 miles. A different problem has risen.
At start up the car idles at 1500 rpm and slowly comes down to 1100 rpm when fully warm. At random times it dips down and idles at 750-800rpm how I had it set to previously, but after moving and coming back to a stop the idle goes back up to 1100. The timing is set correctly to what the manual calls out for (5* btdc, I think). Here is the interesting part, if I ground the pin in the cabin and in the engine bay for idle adjustment, the car idles perfect at 750-800 rpm. As soon as I disconnect one of the grounding wires, it jumps back up to 1100 rpm. This led me to believe that maybe the idle position switch could be bad, so I checked voltage and ohms. Botch checked ok. With tb closed I'm getting about 1.5-3.0 ohms. WIth the throttle cracked open it goes to infinity (the DMM). The voltage is at about 0.0 vdc when closed and 12.xx vdc when open. I did a boost leak and it checked out good. I also tried grounding the idle position switch wire directly, but that didn't change the idle condition. It remained at 1100 rpm.
My question is: what could be causing the ECU to not go into idle mode? What components do the ECU listen to to determine it's at idle? The IPS checks ok, the TPS is set correctly.
One interesting fact: When the ignition key is to on (the engine not running) , I can hear the ISC motor chattering away. The only way that I have gotten it to stop was to disconnect it. It does this at random before I start it a lot of times.
Thank you for all your help!
